1. The slow startup time in question
2. The huge editor software file size. I am not leaving 400mb for "yet another text editor"
3. I had become very dependent on some Sublime plugins for my work and the Atom counterparts were a long ways off being up to par.
The thing that first made me excited about atom was that being built around Chromium I thought we could finally have an editor with a nice Chrome-like web view with real-time update built into it, as a tab or something.
However, I noticed a thread on it in Atom (can't find it now), and it sounded like the core of Atom's security prevented such a thing from ever being built, so it would remain an unfulfilled desire. Oh well.